Field of the Invention
The present invention relates to a heat sealable printing sheet including a sheet-shaped base member, an ink receiving layer having a heat sealability, and a heat sealable layer.
Description of the Related Art
Heretofore, wrapped articles have been widely sold, such as beverages, confectioneries, foods, cigarettes, cassette tapes, and disks. In these articles, packaged objects containing contents are wrapped with a transparent wrapping film. Such packaged objects are provided with such a variety of prints as to bring highly sophisticated preferences and values; for example, a print of a natural sight, seasonable event, or the like in each season to make one feel the season; and a print to add a value as a special gist for a ceremonial occasion or the like. In producing highly value-added wrapped articles, a printed matter has to be altered for each wrapped article.
For example, printing modifications are made as follows. For instance, a fixed part of a printed matter is printed on a packaged object, while only a to-be-altered part of the printed matter is printed on a wrapping film. Then, these two parts are correctly aligned with each other to form a wrapped article. However, since a wrapping film is often printed by gravure printing, the cost per article is high if the number of articles to be printed is small.
Under such a background, inkjet printing has attracted attention as a technique that can be employed for printing of a small number of copies, to which the application of gravure printing is not reasonable. Nevertheless, when a wrapping film is printed by the inkjet process, an ink receiving layer for absorbing an ink needs to be provided in the wrapping film. Further, the ink receiving layer needs to adhere to a heat sealable layer provided on a back surface of the ink receiving layer. Furthermore, the ink receiving layer and the heat sealable layer should be controlled to be kept from adhering to a packaged object during thermal pressure bonding. Japanese Patent Laid-Open No. H10-244749 (1998) discloses a technique related to an ink receiving layer to which a heat sealability is imparted: a printing sheet including an ink receiving layer blended with particulate resin particles obtained from a resin containing an amino group.
However, in the printing sheet disclosed in Japanese Patent Laid-Open No. H10-244749 (1998), since the ink receiving layer is formed of resin particles, it has been difficult to sufficiently ensure the ink absorbability.
Meanwhile, it is also necessary to make a wrapping film less likely to cause a trouble in unwrapping, for example, the film can be torn with a favorable cross section in unwrapping. In general, some wrapping films are provided with a pinch portion which serves as such an opening point for unwrapping as to open the wrapping films surely and easily. However, a wrapping film provided with an ink receiving layer for absorbing an ink has an additional thickness attributed to the ink receiving layer, so that the ink receiving layer may remain as a burr at the torn portion in unwrapping, or the ink receiving layer may peel off from a base member constituting the wrapping film.
Further, a wrapped article as shown in FIG. 3 has to be controlled such that even when a wrapping film is folded at an acute angle, an ink receiving layer needs to be prevented from cracking and peeling off from a base member at the folded portion. However, since the wrapping film provided with the ink receiving layer for absorbing an ink has an additional thickness attributed to the ink receiving layer, the heat sealable printing sheet becomes hard as a whole, and folding may cause the ink receiving layer to peel off from the base member.